A pressure sensor having a corrugated diaphragm according to a prior art is disclosed in U.S. Pat. No. 5,565,629. The pressure sensor includes a casing having a pressure detection chamber for accommodating liquid, a plate shape diaphragm for receiving pressure of a measuring object, and a pressure detection element for detecting pressure of the liquid. The diaphragm is disposed so as to contact the liquid enclosed in the pressure detection chamber. The pressure detection element is disposed in the pressure detection chamber to detect the pressure of the liquid. The pressure of the measuring object is transmitted from the diaphragm to the pressure detection element through the liquid. The circumferential portion of the diaphragm is mounted on the casing. The diaphragm has a corrugate disposed concentrically with the diaphragm and having a half circular cross-section, i.e., an arch shape.
The pressure receiving area of the diaphragm for receiving the pressure becomes large because of the corrugate. Therefore, fluctuation of the pressure of liquid in the pressure detection chamber can be reduced. The fluctuation of the pressure is, for example, caused by temperature change.
In the pressure sensor having the corrugated diaphragm, the corrugate is disposed on almost circumferential side of the diaphragm, i.e., disposed on a circumference of the diaphragm. Here, the circumference of the diaphragm is fixed to the casing.
It is required to minimize a size of the pressure sensor. By this minimization of the sensor, a diameter of the diaphragm, i.e., an area of the diaphragm also becomes small. In this case, an inner pressure of the pressure detection chamber, i.e., the pressure of the liquid applied to the diaphragm per unit area becomes higher. Therefore, characteristic curvature of the pressure sensor between the inner pressure and a variation of the diaphragm deviates from a linear curve, i.e., becomes nonlinear as the inner pressure becomes higher.
Therefore, to minimize the pressure sensor, it is required that the characteristic curvature has high linearity in a range between a low pressure and a high pressure.